Stepping motors may be used, for example, in a moving device, as described in U.S. Pat. No. 6,859,335B1 for positioning optical elements, such as nonlinear crystals or saturable absorbers. The stepping motors may include synchronous motors, in which the rotor is rotated step-by-step by a controlled electromagnetic field. The number of the steps covered by the stepping motor may be counted in stepping motor drives to determine a sufficiently accurate position. Stepping motor drives typically include a large number of mechanical and also electronic components, which can outgas and therefore contribute to damage to the nonlinear crystal or saturable absorber.
The position of a moving device may be determined by a Hall sensor, as described in the dissertation “Miniaturisierte Positioniersysteme mit mehreren Freiheitsgraden auf der Basis monolithischer Strukturen [Miniaturized positioning systems having multiple degrees of freedom on the basis of monolithic structures]” by Uwe Jungnickel (Darmstadt Technical University).
Miniaturized positioning systems and/or miniaturized moving devices are available, in which the adjustment or moving motions are based on the drive of piezo units and/or piezo drivers. Piezo units generally cause a step-by-step drive of the moving parts, in which the length of the incremental step can vary over a relatively wide range, since it is force-dependent. For example, the piezo elements may degrade with time, which leads to a change in the length of the incremental step. In turn, this may lead to a location dependence of the moving device. For instance, the length of the incremental step of a horizontally moving device may deviate from the incremental step of a moving device moving in a vertical or inclined direction. Monitoring or checking the accurate position of the moving device requires using complex, costly, and sensitive path measurement systems.